What are the meanings of graphical symbols including !\ shown in instruction manuals?

They are called Graphical Warning Symbols for Consumers and defined by JIS and other standards as "to inform consumers of cautions, instruction manuals, and other information that can be generally understood without consulting professionals or depending on job training."
These graphical symbols are shown on product bodies, instruction manuals, and package boxes as needed to call attention and encourage proper use.

1. Prohibition

Prohibition

To inform consumers of prohibited use of products.
Read instruction manuals carefully for safe use, avoid the use marked with this graphical symbol, and use watches and clocks properly.

2. Caution

Caution

To call attention to product handling that may cause fire and high temperature. Inside the triangle shows "!" for general warning and other specific graphical symbols in a black color.

Caution

To call attention to general warning. See the table below for examples.

Description of Harm/Damage

Danger

Improper use may cause consumers' death or serious injury and the danger level is high.

Warning

Improper use may cause consumers' death or serious injury.

Caution

Improper use may cause serious injury or physical damage.

3. Directions

To inform customers of instructions that must be followed. 
Read instruction manuals carefully for safe use, follow the instructions marked with this graphical symbol, and use watches and clocks properly.

To inform customers of instructions that must be followed.
Read instruction manuals carefully for safe use, follow the instructions marked with this graphical symbol, and use watches and clocks properly.